1. Field of the Invention:
The present invention relates to the art of continuous papermaking by means of aqueously suspended fiber discharged from a headbox slice opening upon a traveling forming screen or fabric.
2. Description of the Prior Art:
Papermaking stock is an extremely dilute, aqueous slurry of fiber; usually cellulose fiber or blended mixtures of natural and man-made fiber. Fourdrinier papermaking includes the process step of jetting a flow of papermaking stock from the slice opening of a headbox onto the surface of horizontally traveling screen or fabric belt.
As the traveling screen carries the stock flow from the slice jet landing zone, aqueous vehicle, i.e. water, drains through the fabric matrix to leave the fiber suspended on the fabric surface in a consolidated mat.
Between the stock landing zone and the longitudinally displaced point along the screen belt traveling route whereat the mat consolidates, the stock is supported on the screen surface as a liquid pond of diminishing depth. Without lateral containment, lateral pond flow cross-directionally distributes stock towards the screen sides thereby undesirably thickness tapering the resultant paper web edge areas.
To prevent undesirable tapered thickness along the web edges, lateral pond confinement structures called "deckle boards" are positioned above and along the screen edges out from the slice landing zone. Traditionally, deckle boards are bottom sealed to the upper screen surface with fabric or elastomer which, consequently, is a source of friction, drag and wear upon the screen surface.
Additionally, traditional deckle board structure is a source of standing waves in and across the stock pond. When consolidated by aqueous vehicle drainage, these deckle waves cause undesirable fiber concentration, i.e. basis weight, variations in the paper web product.
An object of this invention, therefore, is provision of a deckle structure having no frictional contact with the forming screen and does not propagate or reflect pond waves.